The water pollution situation in China is severe. Many areas have suffered from long-term water pollution problem, which has seriously impaired the health of the residents and the sustainable development of industry. With the implementation of the new environmental law on Jan. 1, 2015, the requirement for deep treatment of wastewater is becoming more and more urgent in China, especially the treatment problem of the non-degradable industrial wastewater.
At present, the biological method formed by combination of aerobic and anaerobic technologies is the cheapest and most effective way to remove organic pollutants, however it is unable to treat the pollutants with high biological toxicity and subsequent physical and chemical processing units are needed. Advanced oxidation method is the most promising deep treatment method, comprising the generation of hydroxyl radicals with strong oxidizing ability through the addition of energy field, light radiation, and reagents, etc., to deeply mineralize the pollutants, the products of which are harmless water and carbon dioxide. Advanced oxidation method includes Fenton oxidation, photocatalysis, ozonation, wet catalytic oxidation, supercritical water oxidation, ultrasonic oxidation, etc. However, there are certain advantages and disadvantages for these various methods. For example, the Fenton oxidation is simple in processing flow and has strong oxidizing ability, but it requires an acidic environment and produces a large amount of iron mud. The photocatalysis is slow in reaction rate and cannot overcome the problem of high cost of industrial application in a short-term. The wet catalytic oxidation requires high temperature and high pressure, which is only suitable for the wastewater treatment process with very high concentration and small water volume. The ozonation is mild in operating condition and has strong oxidizing ability, thus it has found certain applications in the municipal sewage disinfection and industrial wastewater treatment, however, its efficiency and cost are required to be further improved.
There are two ways to improve the efficiency of the ozonation: the development of high performance catalyst and the design of new reaction processes. A large number of papers and patents disclose the development process of high performance ozonation catalyst, for example CN102029165A and CN102049253A published a method for preparing different ozonation catalysts suitable for water treatment, respectively. The new reaction process mainly refers to the coupling of ozone with other reaction separation processes, such as the combination of ozone with ceramic membrane filtration, photocatalysis, and hydrogen peroxide, etc., which can increase the oxidizing ability of the ozonation process to some extent.
CN101497014 discloses a novel ozone-photocatalysis fluidized bed reaction device and a water treatment method which uses at least two devices to regenerate the fluidized catalyst in water with the off-gas ozone through switching the reaction device, which solves the problems of catalyst contamination as well as pollution and waste of the off-gas ozone, etc., however, the utilization efficiency of ozone is low relative to the effect of water treatment.
CN201762164U discloses a method for suspending the activated carbon in the reactor with the gas stripping method, however, it is required to intercept the activated carbon particles when discharging water, and the activated carbon has strong absorption for the ultraviolet light, thus the photocatalytic efficiency is low.
The existing technology employs ozone photocatalysis to treat the industrial wastewater, which will produce a large amount of hydroxyl radicals, and the treatment efficiency will be impacted due to the ineffective annihilation with each other; although the ozone has strong oxidizing effect on the unsaturated bond-containing pollutants, the removal effect on the carboxylic acid intermediate products formed after the cleavage of double bonds is limited. On the other hand, the lifetime of the ultraviolet light tubes for photocatalysis is shorter, therefore the extensive use of ultraviolet light source will increase the treatment cost.
Therefore, there is an urgent need to develop an ozone-photocatalysis reactor in the art, which has higher reaction efficiency, strong processing effect on the sewage and low manufacturing cost.